I had cause to search for information on 'blocking oscillators' today and ended up at a Wikipedia entry :
https://en.wikipedia.org/wiki/Blocking_oscillator
There was a link there to a web page at
www.du.edu/~etuttle/electron/elect37.htm "
by James B. Calvert. An elementary (no mathematics) and informative description of various blocking oscillator circuits, employing BJTs and Triodes."
Unfortunately that link now longer works but this one does :
https://mysite.du.edu/~etuttle/electron/elecindx.htm , and partway down the index is #39, blocking oscillators. As it says, "
Every circuit has been tested in the laboratory".
I got 'lost' in visiting many of the other entries on that index list, and it became a very interesting task although I was well and truly sidetracked by it all. Obviously the author is an amateur operator and several references to the ARRL Handbook are made.
Just as a matter of interest, I found that the root of the 'etuttle web' was actually at
https://mysite.du.edu/~etuttle/ and it was designated as belonging to Dr Elizabeth R Tuttle so where the 'James B Calvert' comes into it is unclear. Note: Just found it..
"
Composed by J. B. Calvert
Created 17 August 2001
Last revised 8 April 2003"
If you want to go adventuring and find out some interesting stuff on vacuum tubes (/ valves) as well as semiconductor use, be prepared to spend some time at this site.
73 Doug VK4ADC
PS Why I want a blocking oscillator circuit will remain undisclosed but have a look at the typical waveform generated..